This invention relates to a process for producing superior quality canned legume products.
Many varieties of dry beans (sometimes called shell beans) are available in pre-cooked, canned form. Such pre-cooked canned beans offer numerous advantages in convenience over uncooked dry beans, which require lengthy soaking and cooking before they can be eaten.
However, the quality of typical canned bean products has been notoriously poor. Typically, canned beans have tough, irritating, paper-like seed coats, mushy or granular textures, and metallic or tin-like off flavors. In addition, some varieties of beans, such as large lima beans, often show a blue-gray discoloration defect referred to as "blue-bellies" when canned according to conventional methods.
Typical procedures for canning legume products consist of inspection of the dry legumes, cleaning, soaking, destoning, blanching, inspection, filling the cans, closing the cans, and processing (retorting) to sterilize and cook the canned legumes. See generally, A. Lopez, "A Complete Course in Canning", volume 2, chapter 7 (10th Ed. 1975).
In addition to quality and appearance problems in the finished product, conventional prior art canning methods for dry beans suffer from a number of other disadvantages. For example, beans must be soaked in the soaking step until they have absorbed an amount of moisture equal to approximately 85% to 110% of their dry weight (46% to 52% moisture). Minimum soaking periods range from eight to fourteen hours, depending upon the type of bean and its initial moisture content and soaking temperature. Soaking times of sixteen hours are typical at room temperature and atmospheric pressure. Hard water is generally unsuitable for soaking, because the dissolved calcium and magnesium compounds in the water will harden the legumes, requiring a longer process to make them edible. With very hard water, it may not be possible to obtain an acceptably tender product.
Careful control of the length of the soaking operation is necessary in conventional processes. The moisture content of dried beans may vary from 9% to as much as 20%. The drier and harder beans absorb moisture more slowly than those with a higher moisture content. If high moisture beans are soaked for too long a period they tend to become soft and, as a result, split and become mushy during processing. The relatively long soaking times required even for beans with higher moisture contents often lead to problems of souring caused by growth of microorganisms in the soaking medium and by enzymatic and biochemical changes in the legume during germination, as a result of hydration.
Due to variations in moisture content of the beans, prior art processes require careful control of the fill-in ratio. The fill-in ratio is the weight ratio of beans to liquid in the can. Beans absorb additional moisture as they cook within the can during the retorting process.
Government regulations require that canned legumes be processed for a sufficient period of time to achieve commercial sterility. Commercial sterility, as used herein, means the practical absence of microorganisms having public health significance, as well as more innocuous organisms, that are capable of reproducing in the food during normal unrefrigerated storage and distribution. Typical processing times in a still retort, by necessity, range anywhere from 45 to 235 minutes at 240.degree. F. depending on can size and sauce formulation. Moreover, it is common practice to overprocess from 10% to 50% more than the time required for sterilization in order to insure that all the beans are completely cooked and that tough beans are tenderized. Unfortunately, such overprocessing exacerbates the problems of split seed coats and mushy, poor quality product.
One of the major innovations in legume-processing technology in recent years has been the so called "quick-cooking" processing method. Although quick-cooking technology has not been generally applied to canned legume products processed in still retorts, it represents a major advance in the preparation of dried, frozen or refrigerated hydrated legume products, and marinated mixed bean salads which are processed in rotary retorts. See generally U.S. Pat. Nos. 3,318,708, 3,352,687, 3,635,728, 3,869,556, and 4,159,351, all to Rockland, et al. Quick-cooking technology involves soaking the beans or other legumes in a special hydrating medium (a "quick-cooking salt solution") containing sodium chloride, a bicarbonate-carbonate buffer combination, and a chelating agent. The process described in the '708 Patent includes the step of alternately applying and releasing a vacuum while the legume seeds are hydrating. In '728, beans are blanched in boiling water for a short period prior to soaking in the hydrating medium. In '351, a number of different bean varieties are treated to render them fully quick-cooking and are heated for a very brief period only to remove undesirable color in the cook water before thermal processing. In that process, a rotary retort is required because beans hydrated in accordance with the prior art and cooked in a still retort, either with or without a post-soak blanch, are soft and unacceptable in texture, flavor, and appearance.
Although quick-cooking technology is known to greatly improve the quality of prepared dried beans and other legumes, it has not been applied to canned beans in general for several reasons. In the first place, the hydration times for quick-cooking processes generally correspond to the required hydration times in conventional canning processes. Thus, quick-cooking technology would result in no savings in time but would increase the production cost because of the necessity of providing special soaking solutions. Moreover, the still retort times during the processing step necessary to achieve a commercially sterile product generally correspond to the time required to cook conventionally processed beans. Those same processing times, however, greatly exceed the processing times required to cook fully processed quick-cooking legumes, and would be expected to produce a greatly overcooked product with split seed coats and a mushy texture.
In light of the foregoing disadvantages of prior art processes, the present invention has several objects, including greatly reducing the long soak period of prior art processes, eliminating the necessity of overcooking canned legumes in order to tenderize them, eliminating blue-bellies, eliminating the necessity of using softened water in the soaking process, reducing the variations necessary in the fill-in ratio, minimizing or eliminating the problems involving souring and metabolism during the soaking process, and greatly improving the texture and quality of the canned product.
Legumes processed in accordance with the present invention have the optimum appearance, texture, flavor and color. There is no other method known that will produce this effect from standard or totally processed quick-cooking beans.